Modern driver assistance systems are increasingly equipped with an electronic traffic sign recognition system, for example to warn the driver when the vehicle exceeds the allowed speed limit. A camera records the area in front of the vehicle and provides respective image data to an image evaluation device, which analyzes and classifies the data using an algorithm to identify traffic signs from it. Such a method is known, for example, from DE 198 52 631 A1. The information from traffic signs identified in this way can then be fed into a driver assistance feature, e.g. as indication of the currently allowed speed limit on the instrument cluster of the vehicle.
Traffic signs are often equipped with additional signs that qualify the meaning of the main sign or restrict it to specific situations.
WO 2008/145545 A1 discloses a method for identifying traffic-relevant information in which the data from a camera sensor and map data of a navigation system are interpreted. Additional signs can be taken into account if their content is included in the map data of the navigation system.
DE 10 2008 057 675 A1 describes a method in which, after identifying a traffic sign, the system looks for an additional sign assigned to the traffic sign at predefined positions (relative to the identified traffic sign). The additional sign is classified by comparison with stored depictions of additional signs, e.g. using a radial basis function.
The disadvantage of this method is that there is any number of variants for time-limiting additional signs, which would either all have to be stored or the driver only receives the additional information that the “traffic sign applies at limited times” because the content information of the additional sign cannot be recognized.
Since such traffic sign recognition systems treat additional signs purely as pictograms, such additional signs are viewed and classified as a whole, that is, as an image pattern. This means that all “time information” falls into one and the same class that cannot be further differentiated without obtaining additional knowledge, e.g. from a navigation system.